Many types of opto-electronic modules comprise a number of separate optical and electrical components that require precise placement relative to one another. A silicon (or glass) carrier substrate (sometimes referred to as an interposer) is generally used as a support structure for these components and may, at times, also provide the desired electrical or optical signal paths between selected components. In other arrangements, the optical and electrical components may be directly placed on and within a silicon surface layer of a silicon-on-insulator (SOI)-based optical platform. Regardless of the structure of the support arrangement, optical alignment between various optical components is required to ensure that the integrity of the optical signal path is maintained.
As the size of opto-electronic components continues to shrink, the need to place them on an interposer (or other supporting substrate member) with improved alignment accuracy increases. This is particularly true in optics where components such as lenses and fiber/waveguide connectors form part of an optical signal path and inter-component alignment is necessary to maintain the integrity of the signal path. For example, in a silicon photonic assembly, components such as microlenses and optical fibers may need to be aligned to one another with sub-100 nm positional accuracy as they are attached to a common substrate, such as an interposer or silicon-on-insulator (SOI) substrate.
While the ability to accurately position these components on a substrate is a necessary requirement of the fabrication process, the maintenance of these positions over the lifetime of the assembly is also important. It is quite possible that a given assembly will be subjected to variations in temperature, humidity and the like over its lifetime, where these environmental changes may degrade the quality of the adhesive bond and cause one component to shift relative to another. One way to address the lifetime issue is to utilize as thin a bond line as possible in the original attachment process (a “bond line” being defined as the thickness of the adhesive between the two surfaces being bonded). It has been found that bond lines on the order of tens of microns will increase the lifetime stability of micro-component assemblies. However, this relatively thin bond line has presented problems in terms of the friction-based restriction of the flow of the adhesive (i.e., molecular flow regime), associated with the relatively large surface areas to be joined relative to the total volume (relatively small) of the adhesive. This frictional problem associated with the small amount of adhesive material then also limits the amount of post-placement adjustment of the micro-component that may be performed, eliminating the possibility of performing active or quasi-active alignment in many optical or opto-electronic systems. Indeed, as the bond line reduces to a size of less than five microns, it becomes increasingly difficult to displace the liquid material between the lens and substrate (i.e., hydrostatic compression).